High frequency attenuator



1955 R. M. WALKER HIGH FREQUENCY ATTENUATOR Filed DeC. 23, 1947HIGH-L055 MATERIAL LOW -L055 MATERIAL INVENTOR. WALKER RICHARD M BYWBWATTORNEY United States Patent cc HIGH FREQUENCY ATTENUATOR Richard M.Walker, Dorchester, Mass., assignor to Sylvania Electric Products Inc.,Salem, Mass., a corporation of Massachusetts Application December 23,194.7, Serial N 0. 793,487 7 Claims. (Cl. 333-81) This invention relatesto energy controlling pads for hollow waveguides.

The invention provides an eflicient means for controlling high frequencyenergy by introducing in the waveguide, pads of various types ofmaterial having different energy controlling characteristics, andutilizing the combined effects of the different materials to attenuatethe energy they intercept. v

It is an object of the invention to provide an efficient, stable andreadily adjustable means for controlling the high frequency energywithin a waveguide.

A further object of the invention is to provide high frequency energycontrolling means which is protected from mechanical breakage thuspermitting the use of frangible material for the controlling pads.

A further object of the invention is to provide an attenuator device forhigh frequency power conductors which is of compact structure.

Other objects and features will more fully appear from the followingdescription and will be particularly pointed out in the claims.

To present a better understanding of the invention a particularembodiment thereof will be described and illustrated in the drawings inwhich:

Figure 1 is a perspective view of a waveguide having a preferredembodiment of the invention therein.

Figure 2 is a longitudinal section through the device shown in Figure l.

The invention may be used in any hollow waveguide system. By way ofillustration it is shown in connection with a hollow rectangularwaveguide 1 of conventional type having a rectangular channel 2 withinwhich is received an energy controlling pad 3. The pad may be composedof two or more different materials. As shown in the drawing the pad iscomposed of a section of high loss material 4 and a section of low lossmaterial 5. The two sections of material fill the waveguide channel andwhen cemented therein form a pressure tight seal which may be useful forcertain applications of the invention. By choosing materials of theproper kind and varying the dimensions of the sections of material used,definite control of energy may be established.

Another important feature of the invention is the use of pad sectionswhich are of right angled prismatic form.

As shown in the drawing the portion 4 has a thickness dimensionsubstantially equal to the thickness of the material 5. The two sections4 and 5 fill the waveguide from side wall to side wall. The section 4 ofhigh loss material is smaller than the section 5 and is placed on top ofthe section 5 and centrally positioned thereon lengthwise of thewaveguide. The difference in lengthwise dimensions between the twosections is such that the front edges of section 5 project beyond thefront edges of the section 4 an amount equal to a quarterguide-wavelength at the operating frequency or some odd number ofquarter guide-wavelengths. The input end of the pad, desirably but notnecessarily, being of symmetrical design with that of the output end,the energy conveying line is matched 2,722,661 Fatented Nov. 1, 1955from both ends. The degree of attenuation caused by the pad may bevaried by lengthening or shortening the dimension 6.

The principles of the invention provide forthe fabrication of the pad bybuilding it up from a plurality of sections each of which may be made ofa material having the same or different electrical characteristics. Thedimensions of each element may also be varied asabove stated. It willthus be seen that a wide variety of characteristics may be created tofulfill substantially all circuit requirements.

The practice of the present invention embodies other advantages forexample, the resulting pad structure is mechanically stronger than thoseof conventional form.

Prior to the present invention attenuator'pads have been constructed inwedge form having very thin fragile edges which are difiicult toassemble in a waveguide and operate'without breakage. The materials usedfor the elements 4 and 5 may be selected from a series of high and lowloss polyiron compounds, carborundum, durez or like material. Thesematerials are frangible in character which tends to increase thetendency for breakage to occur particularly in thin sections. Thegeometrical form of the pad elements therefore becomes an importantfactor inthe design of a pad. The pad elements in the present inventionare right angled prisms which are relatively easy to form and do notpresent any delicate portions subject to breakage. Moreover by properselection of materials for the pad elements each element can beproportioned to give the required electrical characteristics and also beof substantial thickness and therefore not subject to breakage.

A further advantage of the present invention is that the pads can berelatively compact in length which is of great advantage in constructingmicrowave apparatus.

In the form of the invention described herein the upper pad section 4 isof high loss material and the section 5 is of low loss material. Inoperation when a high frequency current is fed into the waveguide fromthe left it meets the pad elements 4 and 5 and passes therethrough aportion of its total power being absorbed by the pad. A certain amountof the power is reflected from the front faces of the pad sections. Dueto the spacing of these faces the power reflected from one is shifted inphase from the other. The total amount of reflected power is thuscancelled out thus avoiding the undesirable effects caused by thereflected energy.

An attenuator pad constructed according to the invention, in addition tothe qualities above pointed out, provides broad band matching abilityand in operation maintains its degree of attenuation over a relativelywide range of frequencies.

What I claim is:

1. In combination with a hollow rectangular waveguide forelectromagnetic waves, an attenuator pad filling the guide channel saidpad comprising a plurality of superposed sections having differentenergy absorbing characteristics and of right angle prism formpresenting end faces extending transversely of said channel an end faceof the one of said sections of lower energy absorbing characteristicbeing advanced with respect to the others whereby the phase shiftedcomponents of power reflected from said faces are cancelled.

2. An attenuator pad for waveguides having the elements defined in claim1 and in which the adjacent end faces of the pad sections are spacedapart one quarter guide-wavelength at the operating frequency.

3. An attenuator pad for waveguides having the elements defined in claim1 and in which the adjacent end faces of the pad sections are spacedapart an odd number of quarter guide-wavelengths at the operatingfrequency.

4. An attenuator pad for waveguides for electromagnefic waves comprisinga plurality of flat right angled prismatic sections of power absorbingmaterial of differ ent lengths superimposed lengthwise of said waveguideand laterally filling the channel thereof, each section having difierentenergy absorbing characteristics and presenting end faces disposed atright angles to the axis of said channel, said sections being soarranged thatthe conformation of both ends of the pad are the same, eachend of the pad having the end face of said section of lower energyabsorbing characteristic extending lengthwise one quarterguide-wavelength beyond the adjacent faces of the other section.

5. In a dielectric waveguide, a pad of absorptive material disposedwithin said guide and substantially entirely displacing the normaldielectric thereof and for a predetermined distance in the direction ofwave propagation of said guide, said pad including a plurality ofsuperimposed sections of energy absorbing material, said sections havingtheir end faces normal to said direction of wave propagation, one ofsaid plurality of sections being of higher absorptive characteristicsand shorter in length than another section and the end faces of said onesection being displaced with respect to the adjacent end faces of saidother a distance equal to an odd multiple, including unity, of onequarter guide wave length.

6. In a dielectric waveguide, a pad of absorptive material disposedwithin said guide and substantially entirely displacing the normaldielectric thereof and for a predetermined distance in the direction ofwave propagation of said guide, said pad including a pair of superposedsections of energy absorbing material, said sections having their endfaces normal to said direction of propagation, one of said sectionsbeing of higher absorptive characteristics and shorter in length thanthe other section and the end faces of said one portion being displacedwith respect to the adjacent end faces of said other a distance equal toan odd multiple, including unity, of one quarter waveguide length.

7. In a dielectric waveguide, a pad of absorptive material disposedwithin said guide and substantially entirely displacing the normaldielectric thereof and for a predetermined distance in the direction ofwave propagation of said guide, said pad including a pair of superposedsections of energy absorbing material, said sections having their endfaces normal to said direction of propagation, one of said sectionsbeing of higher absorptive characteristics and shorter-in length thanthe other section and the end faces of said one portion being displacedwith respect to the next-adjacent end faces of said other a distanceequal to an odd multiple, including unity, of one quarter waveguidelength, the absorptive characteristics of said sections being so relatedto the lengths of said sections that components of power reflected fromsaid faces are of equal amplitude and opposite phase relationship.

References Cited in the file of this patent UNITED STATES PATENTS2,409,599 Tiley Oct. 15, 1946 2,411,534 Fox Nov. 26, 1946 2,430,130Linder Nov. 4, 1947 2,449,182 Sontheimer Sept. 14, 1948 2,531,194 BowenNov. 21, 1950 2,538,771 Feenberg Jan. 23, 1951 2,567,210 Hupsey Sept.11, 1951 OTHER REFERENCES Publication I: Publication Board PublicationP, B. No. 6595 declassified January 31, 1946. Copy in the Library ofCongress.

Publication II: Bibliography of Scientific and Industrial Reports, vol.1, No. 20, May 24, 1946. Published by the O. T. S'. Department ofCommerce.

